There was a lot of crossover in the "Oxbridge Mafia" actors and writers in shows that started with Beyond The Fringe and ended with The Goodies. They usually fed off each other and versions of sketches and songs appeared in several shows. Nobody could accuse any of them of plagiarism. Maybe recycling.
The Class Sketch, originally from The Frost Report, was reworked several times in The Two Ronnies and finally in the BBC Millennium programme. Several sketches in How to Irritate People was reworked or even performed almost unchanged by Monty Python.
If you read the excellent book From Fringe to Flying Circus by Roger Wilmut you'll see just how much crossover there was.
Cheers
David